The invention relates generally to graphics processing and more particularly to an integrated circuit for graphics processing which includes a configurable display interface and a method therefore.
Computers are used in many applications. As computing systems continue to evolve, the graphical display characteristics of computing systems become more and more advanced. In order to convey the required data to these advanced display systems, higher transmission data rates between the circuitry which generates the display data and the actual display are required.
In addition to providing a high rate of data transmission, the interface between the processing system which produces the display data and the actual display device must provide transmission capabilities that are reliable and also that do not interfere with other elements internal to and external to the computing system. This is especially true in the transmission of video data between a host processing system and flat-panel displays, which include liquid crystal displays (LCD""s). The data rates required to adequately drive an LCD display are very high. When this data is transmitted in a digital fashion, the high-speed switching of the signal lines can result in electromagnetic interference (EMI) that can have detrimental effects on other portions of the system.
In order to meet these transmission needs, external circuits that receive digital information and convert it to analog differential voltage transmissions have been developed. These external circuits perform this conversion utilizing an encoding scheme that reduces signal transitions and power consumption, and also provides DC balancing on the transmission lines to ensure accurate recovery of the data on the receiving end. One such transmission standard, transition minimized differential signaling (TMDS) has been developed to suit the needs of many LCD displays.
Unfortunately such external transmission solutions require large data interfaces with host processors that produce the image data for display. These complex interfaces increase production cost and also contribute to EMI emissions in circuits which utilize a TMDS interface with a graphics processing integrated circuit, or chip. Additional problems with the interface between the graphics processing chip and the TMDS transmitting circuitry include cross talk, signal skew, and intertrace balancing. All of these limitations can place a ceiling on the maximum data rates that are achievable in a system. Thus, the operating frequency of such a combined circuit can be restricted by these inherent limitations.
Typical TMDS transmission circuits are mounted on printed circuit boards with a graphics circuit that provides the image data to be encoded and transmitted. On these printed circuit boards, control signals that are included in the TMDS transmission stream are typically configured using resistors that are mounted to the printed circuit board. In order to change the settings of the control signals included in the stream, these resistors have to be replaced.
Similarly, the swing amplitude of the differential signals utilized in a TMDS system is configured using external resistors mounted to the printed circuit board. Often, the swing amplitude of a TMDS transmitter may have to be adjusted to suit different cable lengths that connect the transmitting circuitry to the receiver in the display device.
In order to adjust for different cable lengths and transmission characteristics, these external resistors have to be replaced to alter the swing amplitude of the transmission signals. Thus, the requirement of adjusting actual physical circuit components in order to change the swing amplitude or the value of control signals broadcast with the transmitted data is both cumbersome and limiting in the effective use of current TMDS transmitters.
Therefore, a need exists for a data transmission system between the graphic circuitry which creates the signals to drive the display, and the actual display device. Such a transmission system should allow for flexible configuration of control signals included in the system and also flexible configuration of the drive strength of the transmitter. In addition to this, the transmission system should eliminate complex interchip digital interfaces, thus reducing EMI emissions and allowing data rates that are not achievable in prior art systems.